Make BlobReadChannel should fail if content is updated

gcloud-java-storage/src/main/java/com/google/gcloud/spi/DefaultStorageRpc.java

@@ -410,8 +410,8 @@ public void onFailure(GoogleJsonError e, HttpHeaders responseHeaders) {
   }
 
   @Override
-  public byte[] read(StorageObject from, Map<Option, ?> options, long position, int bytes)
-      throws StorageException {
+  public Tuple<String, byte[]> read(StorageObject from, Map<Option, ?> options, long position,
+      int bytes) throws StorageException {
     try {
       Get req = storage.objects()
           .get(from.getBucket(), from.getName())
@@ -420,12 +420,13 @@ public byte[] read(StorageObject from, Map<Option, ?> options, long position, in
           .setIfMetagenerationNotMatch(IF_METAGENERATION_NOT_MATCH.getLong(options))
           .setIfGenerationMatch(IF_GENERATION_MATCH.getLong(options))
           .setIfGenerationNotMatch(IF_GENERATION_NOT_MATCH.getLong(options));
-      MediaHttpDownloader downloader = req.getMediaHttpDownloader();
-      downloader.setContentRange(position, Ints.checkedCast(position + bytes - 1));
-      downloader.setDirectDownloadEnabled(true);
+      StringBuilder range = new StringBuilder();
+      range.append("bytes=").append(position).append("-").append(position + bytes - 1);
+      req.getRequestHeaders().setRange(range.toString());
       ByteArrayOutputStream output = new ByteArrayOutputStream();
-      req.executeMediaAndDownloadTo(output);
-      return output.toByteArray();
+      req.executeMedia().download(output);
+      String etag = req.getLastResponseHeaders().getETag();
+      return Tuple.of(etag, output.toByteArray());
     } catch (IOException ex) {
       throw translate(ex);
     }

gcloud-java-storage/src/main/java/com/google/gcloud/spi/StorageRpc.java

@@ -249,7 +249,7 @@ StorageObject compose(Iterable<StorageObject> sources, StorageObject target,
   byte[] load(StorageObject storageObject, Map<Option, ?> options)
       throws StorageException;
 
-  byte[] read(StorageObject from, Map<Option, ?> options, long position, int bytes)
+  Tuple<String, byte[]> read(StorageObject from, Map<Option, ?> options, long position, int bytes)
       throws StorageException;
 
   String open(StorageObject object, Map<Option, ?> options) throws StorageException;

gcloud-java-storage/src/main/java/com/google/gcloud/storage/BlobReadChannel.java

@@ -26,9 +26,8 @@
 /**
  * A channel for reading data from a Google Cloud Storage object.
  *
- * Implementations of this class may buffer data internally to reduce remote calls.
- *
- * This class is @{link Serializable}, which allows incremental reads.
+ * Implementations of this class may buffer data internally to reduce remote calls. This interface
+ * implements {@link Restorable} to allow saving the reader's state to continue reading afterwards.
  */
 public interface BlobReadChannel extends ReadableByteChannel, Closeable,
     Restorable<BlobReadChannel> {

gcloud-java-storage/src/main/java/com/google/gcloud/storage/BlobReadChannelImpl.java

@@ -23,6 +23,7 @@
 import com.google.gcloud.RestorableState;
 import com.google.gcloud.RetryHelper;
 import com.google.gcloud.spi.StorageRpc;
+import com.google.gcloud.spi.StorageRpc.Tuple;
 
 import java.io.IOException;
 import java.io.Serializable;
@@ -41,6 +42,7 @@ class BlobReadChannelImpl implements BlobReadChannel {
   private final StorageOptions serviceOptions;
   private final BlobId blob;
   private final Map<StorageRpc.Option, ?> requestOptions;
+  private String lastEtag;
   private int position;
   private boolean isOpen;
   private boolean endOfStream;
@@ -117,12 +119,19 @@ public int read(ByteBuffer byteBuffer) throws IOException {
       }
       final int toRead = Math.max(byteBuffer.remaining(), chunkSize);
       try {
-        buffer = runWithRetries(new Callable<byte[]>() {
+        Tuple<String, byte[]> result = runWithRetries(new Callable<Tuple<String, byte[]>>() {
           @Override
-          public byte[] call() {
+          public Tuple<String, byte[]> call() {
             return storageRpc.read(storageObject, requestOptions, position, toRead);
           }
         }, serviceOptions.retryParams(), StorageImpl.EXCEPTION_HANDLER);
+        if (lastEtag != null && !Objects.equals(result.x(), lastEtag)) {
+          StringBuilder messageBuilder = new StringBuilder();
+          messageBuilder.append("Blob ").append(blob).append(" was updated while reading");
+          throw new StorageException(0, messageBuilder.toString(), false);
+        }
+        lastEtag = result.x();
+        buffer = result.y();
       } catch (RetryHelper.RetryHelperException e) {
         throw StorageException.translateAndThrow(e);
       }
@@ -152,6 +161,7 @@ static class StateImpl implements RestorableState<BlobReadChannel>, Serializable
     private final StorageOptions serviceOptions;
     private final BlobId blob;
     private final Map<StorageRpc.Option, ?> requestOptions;
+    private final String lastEtag;
     private final int position;
     private final boolean isOpen;
     private final boolean endOfStream;
@@ -161,6 +171,7 @@ static class StateImpl implements RestorableState<BlobReadChannel>, Serializable
       this.serviceOptions = builder.serviceOptions;
       this.blob = builder.blob;
       this.requestOptions = builder.requestOptions;
+      this.lastEtag = builder.lastEtag;
       this.position = builder.position;
       this.isOpen = builder.isOpen;
       this.endOfStream = builder.endOfStream;
@@ -171,6 +182,7 @@ static class Builder {
       private final StorageOptions serviceOptions;
       private final BlobId blob;
       private final Map<StorageRpc.Option, ?> requestOptions;
+      private String lastEtag;
       private int position;
       private boolean isOpen;
       private boolean endOfStream;
@@ -182,6 +194,11 @@ private Builder(StorageOptions options, BlobId blob, Map<StorageRpc.Option, ?> r
         this.requestOptions = reqOptions;
       }
 
+      Builder lastEtag(String lastEtag) {
+        this.lastEtag = lastEtag;
+        return this;
+      }
+
       Builder position(int position) {
         this.position = position;
         return this;
@@ -215,6 +232,7 @@ static Builder builder(
     @Override
     public BlobReadChannel restore() {
       BlobReadChannelImpl channel = new BlobReadChannelImpl(serviceOptions, blob, requestOptions);
+      channel.lastEtag = lastEtag;
       channel.position = position;
       channel.isOpen = isOpen;
       channel.endOfStream = endOfStream;
@@ -224,8 +242,8 @@ public BlobReadChannel restore() {
 
     @Override
     public int hashCode() {
-      return Objects.hash(serviceOptions, blob, requestOptions, position, isOpen, endOfStream,
-          chunkSize);
+      return Objects.hash(serviceOptions, blob, requestOptions, lastEtag, position, isOpen,
+          endOfStream, chunkSize);
     }
 
     @Override
@@ -240,6 +258,7 @@ public boolean equals(Object obj) {
       return Objects.equals(this.serviceOptions, other.serviceOptions)
           && Objects.equals(this.blob, other.blob)
           && Objects.equals(this.requestOptions, other.requestOptions)
+          && Objects.equals(this.lastEtag, other.lastEtag)
           && this.position == other.position
           && this.isOpen == other.isOpen
           && this.endOfStream == other.endOfStream

gcloud-java-storage/src/main/java/com/google/gcloud/storage/BlobWriteChannel.java

@@ -26,8 +26,8 @@
  * A channel for writing data to a Google Cloud Storage object.
  *
  * Implementations of this class may further buffer data internally to reduce remote calls. Written
- * data will only be visible after calling {@link #close()}. This class is serializable, to allow
- * incremental writes.
+ * data will only be visible after calling {@link #close()}. This interface implements
+ * {@link Restorable} to allow saving the writer's state to continue writing afterwards.
  */
 public interface BlobWriteChannel extends WritableByteChannel, Closeable,
     Restorable<BlobWriteChannel> {

gcloud-java-storage/src/main/java/com/google/gcloud/storage/Storage.java

@@ -33,6 +33,7 @@
 import java.io.InputStream;
 import java.io.Serializable;
 import java.net.URL;
+import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
@@ -1405,14 +1406,20 @@ private static void checkContentType(BlobInfo blobInfo) throws IllegalArgumentEx
   BatchResponse apply(BatchRequest batchRequest);
 
   /**
-   * Return a channel for reading the blob's content.
+   * Return a channel for reading the blob's content. The blob's latest generation is read. If the
+   * blob changes while reading (i.e. {@link BlobInfo#etag()} changes), subsequent calls to
+   * {@link BlobReadChannel#read(ByteBuffer)} may throw {@link StorageException}.
    *
    * @throws StorageException upon failure
    */
   BlobReadChannel reader(String bucket, String blob, BlobSourceOption... options);
 
   /**
-   * Return a channel for reading the blob's content.
+   * Return a channel for reading the blob's content. If {@code blob.generation()} is set
+   * data corresponding to that generation is read. If {@code blob.generation()} is {@code null}
+   * the blob's latest generation is read. If the blob changes while reading (i.e.
+   * {@link BlobInfo#etag()} changes), subsequent calls to {@link BlobReadChannel#read(ByteBuffer)}
+   * may throw {@link StorageException}.
    *
    * @throws StorageException upon failure
    */

gcloud-java-storage/src/test/java/com/google/gcloud/storage/BlobReadChannelImplTest.java

@@ -19,7 +19,6 @@
 import static org.easymock.EasyMock.anyObject;
 import static org.easymock.EasyMock.createMock;
 import static org.easymock.EasyMock.expect;
-import static org.easymock.EasyMock.expectLastCall;
 import static org.easymock.EasyMock.replay;
 import static org.easymock.EasyMock.verify;
 import static org.junit.Assert.assertArrayEquals;
@@ -46,7 +45,7 @@ public class BlobReadChannelImplTest {
 
   private static final String BUCKET_NAME = "b";
   private static final String BLOB_NAME = "n";
-  private static final BlobId BLOB_ID = BlobId.of(BUCKET_NAME, BLOB_NAME);
+  private static final BlobId BLOB_ID = BlobId.of(BUCKET_NAME, BLOB_NAME, -1L);
   private static final Map<StorageRpc.Option, ?> EMPTY_RPC_OPTIONS = ImmutableMap.of();
   private static final int DEFAULT_CHUNK_SIZE = 2 * 1024 * 1024;
   private static final int CUSTOM_CHUNK_SIZE = 2 * 1024 * 1024;
@@ -88,7 +87,7 @@ public void testReadBuffered() throws IOException {
     ByteBuffer firstReadBuffer = ByteBuffer.allocate(42);
     ByteBuffer secondReadBuffer = ByteBuffer.allocate(42);
     expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
-        .andReturn(result);
+        .andReturn(StorageRpc.Tuple.of("etag", result));
     replay(storageRpcMock);
     reader.read(firstReadBuffer);
     reader.read(secondReadBuffer);
@@ -107,10 +106,11 @@ public void testReadBig() throws IOException {
     byte[] secondResult = randomByteArray(DEFAULT_CHUNK_SIZE);
     ByteBuffer firstReadBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
     ByteBuffer secondReadBuffer = ByteBuffer.allocate(42);
-    storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE);
-    expectLastCall().andReturn(firstResult);
-    storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, DEFAULT_CHUNK_SIZE, CUSTOM_CHUNK_SIZE);
-    expectLastCall().andReturn(secondResult);
+    expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
+        .andReturn(StorageRpc.Tuple.of("etag", firstResult));
+    expect(storageRpcMock.read(
+        BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, DEFAULT_CHUNK_SIZE, CUSTOM_CHUNK_SIZE))
+            .andReturn(StorageRpc.Tuple.of("etag", secondResult));
     replay(storageRpcMock);
     reader.read(firstReadBuffer);
     reader.read(secondReadBuffer);
@@ -125,7 +125,7 @@ public void testReadFinish() throws IOException {
     byte[] result = {};
     ByteBuffer readBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
     expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
-        .andReturn(result);
+        .andReturn(StorageRpc.Tuple.of("etag", result));
     replay(storageRpcMock);
     assertEquals(-1, reader.read(readBuffer));
   }
@@ -137,7 +137,7 @@ public void testSeek() throws IOException {
     byte[] result = randomByteArray(DEFAULT_CHUNK_SIZE);
     ByteBuffer readBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
     expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 42, DEFAULT_CHUNK_SIZE))
-        .andReturn(result);
+        .andReturn(StorageRpc.Tuple.of("etag", result));
     replay(storageRpcMock);
     reader.read(readBuffer);
     assertArrayEquals(result, readBuffer.array());
@@ -166,16 +166,42 @@ public void testReadClosed() {
     }
   }
 
+  @Test
+  public void testReadGenerationChanged() throws IOException {
+    BlobId blobId = BlobId.of(BUCKET_NAME, BLOB_NAME);
+    reader = new BlobReadChannelImpl(options, blobId, EMPTY_RPC_OPTIONS);
+    byte[] firstResult = randomByteArray(DEFAULT_CHUNK_SIZE);
+    byte[] secondResult = randomByteArray(DEFAULT_CHUNK_SIZE);
+    ByteBuffer firstReadBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
+    ByteBuffer secondReadBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
+    expect(storageRpcMock.read(blobId.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
+        .andReturn(StorageRpc.Tuple.of("etag1", firstResult));
+    expect(storageRpcMock.read(
+        blobId.toPb(), EMPTY_RPC_OPTIONS, DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE))
+            .andReturn(StorageRpc.Tuple.of("etag2", firstResult));
+    replay(storageRpcMock);
+    reader.read(firstReadBuffer);
+    try {
+      reader.read(secondReadBuffer);
+      fail("Expected BlobReadChannel read to throw StorageException");
+    } catch (StorageException ex) {
+      StringBuilder messageBuilder = new StringBuilder();
+      messageBuilder.append("Blob ").append(blobId).append(" was updated while reading");
+      assertEquals(messageBuilder.toString(), ex.getMessage());
+      // expected
+    }
+  }
+
   @Test
   public void testSaveAndRestore() throws IOException, ClassNotFoundException {
     byte[] firstResult = randomByteArray(DEFAULT_CHUNK_SIZE);
     byte[] secondResult = randomByteArray(DEFAULT_CHUNK_SIZE);
     ByteBuffer firstReadBuffer = ByteBuffer.allocate(42);
     ByteBuffer secondReadBuffer = ByteBuffer.allocate(DEFAULT_CHUNK_SIZE);
     expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
-        .andReturn(firstResult);
+        .andReturn(StorageRpc.Tuple.of("etag", firstResult));
     expect(storageRpcMock.read(BLOB_ID.toPb(), EMPTY_RPC_OPTIONS, 42, DEFAULT_CHUNK_SIZE))
-        .andReturn(secondResult);
+        .andReturn(StorageRpc.Tuple.of("etag", secondResult));
     replay(storageRpcMock);
     reader = new BlobReadChannelImpl(options, BLOB_ID, EMPTY_RPC_OPTIONS);
     reader.read(firstReadBuffer);

gcloud-java-storage/src/test/java/com/google/gcloud/storage/ITStorageTest.java

@@ -49,6 +49,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Random;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -730,6 +731,39 @@ public void testReadChannelFail() throws IOException {
     assertTrue(storage.delete(BUCKET, blobName));
   }
 
+  @Test
+  public void testReadChannelFailUpdatedGeneration() throws IOException {
+    String blobName = "test-read-blob-fail-updated-generation";
+    BlobInfo blob = BlobInfo.builder(BUCKET, blobName).build();
+    Random random = new Random();
+    int chunkSize = 1024;
+    int blobSize = 2 * chunkSize;
+    byte[] content = new byte[blobSize];
+    random.nextBytes(content);
+    BlobInfo remoteBlob = storage.create(blob, content);
+    assertNotNull(remoteBlob);
+    assertEquals(blobSize, (long) remoteBlob.size());
+    try (BlobReadChannel reader = storage.reader(blob.blobId())) {
+      reader.chunkSize(chunkSize);
+      ByteBuffer readBytes = ByteBuffer.allocate(chunkSize);
+      int numReadBytes = reader.read(readBytes);
+      assertEquals(chunkSize, numReadBytes);
+      assertArrayEquals(Arrays.copyOf(content, chunkSize), readBytes.array());
+      try (BlobWriteChannel writer = storage.writer(blob)) {
+        byte[] newContent = new byte[blobSize];
+        random.nextBytes(newContent);
+        int numWrittenBytes = writer.write(ByteBuffer.wrap(newContent));
+        assertEquals(blobSize, numWrittenBytes);
+      }
+      readBytes = ByteBuffer.allocate(chunkSize);
+      reader.read(readBytes);
+      fail("StorageException was expected");
+    } catch(StorageException ex) {
+      // expected
+    }
+    assertTrue(storage.delete(BUCKET, blobName));
+  }
+
   @Test
   public void testWriteChannelFail() throws IOException {
     String blobName = "test-write-channel-blob-fail";

gcloud-java-storage/src/test/java/com/google/gcloud/storage/StorageImplTest.java

@@ -1030,7 +1030,7 @@ public void testReaderWithOptions() throws IOException {
     byte[] result = new byte[DEFAULT_CHUNK_SIZE];
     EasyMock.expect(
         storageRpcMock.read(BLOB_INFO2.toPb(), BLOB_SOURCE_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
-        .andReturn(result);
+        .andReturn(StorageRpc.Tuple.of("etag", result));
     EasyMock.replay(storageRpcMock);
     storage = options.service();
     BlobReadChannel channel = storage.reader(BUCKET_NAME1, BLOB_NAME2, BLOB_SOURCE_GENERATION,
@@ -1045,7 +1045,7 @@ public void testReaderWithOptionsFromBlobId() throws IOException {
     byte[] result = new byte[DEFAULT_CHUNK_SIZE];
     EasyMock.expect(
         storageRpcMock.read(BLOB_INFO1.blobId().toPb(), BLOB_SOURCE_OPTIONS, 0, DEFAULT_CHUNK_SIZE))
-        .andReturn(result);
+        .andReturn(StorageRpc.Tuple.of("etag", result));
     EasyMock.replay(storageRpcMock);
     storage = options.service();
     BlobReadChannel channel = storage.reader(BLOB_INFO1.blobId(),